Ever since I began coding in C, I was taught that
for(int i=0;i<10;++i)
...
worked in C++, but in C you must declare the variable outside of the for loop like so:
int i;
for(i=0;i<10;++i)
...
I specifically remember this being a problem because I was used to C++ for loops when I began coding in C.
But today I was reading the December 2010 draft of the C11 standard, and it defined the for loop as
"for ( clause-1 ; expression-2 ; expression-3 ) statement"
and in it's description of syntax it noted:
If clause-1 is a declaration, the scope of any identifiers it declares is the remainder of the declaration and the entire loop.
THEN I did a test and realized that my gcc (Debian 8.3.0) compiles for loops in the C++ style in -std=c99, AND in -std=c11 mode with no warnings even with the -Wall flag.
Is this a gcc extension, or has C supported this type of loop for a while and I just didn't notice?
It was standardized in C99
from: https://en.cppreference.com/w/c/language/for
(C99) If it is a declaration, it is in scope in the entire loop body, including the remainder of init_clause, the entire cond_expression, the entire iteration_expression and the entire loop_statement. Only auto and register storage classes are allowed for the variables declared in this declaration.